ANCHORAGE, Alaska (Reuters) - Alaska officials said on Tuesday they were investigating BP Plc's local unit due to a spate of fires at oil-field facilities, which come after two years of scrutiny over safety at BP's U.S. operations.

A flaring event on Monday at the Lisburne field's production facility was the fourth BP fire on Alaska's North Slope in the past month, a troubling pattern that could result in some new rules, state officials said.

The state has called the managers of BP Exploration (Alaska) Inc, including president Doug Suttles, into meetings to see if there are management, operations or structural problems at BP's oil fields, said Tom Irwin, commissioner of the state Department of Natural Resources.

"We want to have answers to these questions of what's going on on the North Slope," Irwin said at the news conference.

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The incidents included a natural gas release at a gathering center at the Prudhoe Bay field, a generator fire at the Badami field and a turbine compressor fire at a Prudhoe Bay flow station, as well as Monday's event at Lisburne, Irwin said.

"You can't ignore four. You just can't. We can't ignore one. But when it gets to four, in my own mind if I were the public, I'd be saying, Gee, what's going on?"' he said. "How many times has a flare ignited in history that's led to a real serious problem? We want to make sure that doesn't happen."

None of the fires caused injuries, and only an August 6 blaze at Prudhoe Bay's Gathering Center No. 1 hit production. BP has started bringing back the resulting 5,000 barrels per day of lost production, said Jonne Slemons, head of the state's new Petroleum Systems Integrity Office.

A BP spokesman said the company has cooperated with state officials and would continue to do so.

"We have a large oil field. Fires are regrettable, but they do happen. That's why we have safety systems, training programs and multiple layers of protection," said BP's Daren Beaudo. "These systems worked in every incident, and no one was hurt."

Monday's incident occurred when liquids were pushed into an already-burning safety flare and spilled into a flare pit, Beaudo said. That happened when a maintenance device, known as a pig, was being run through a new pipeline, he said.

Any production impact from the fires has been minimal, "within normal operating swings," he said.

BP's operations in Alaska have been under greater scrutiny since corrosion-caused pipeline spills caused a partial shutdown last year at Prudhoe Bay, the largest U.S. oil field.

At a hearing in May, congressional Democrats accused BP of deliberately underspending on maintenance and corrosion prevention at Prudhoe Bay, a charge rejected by BP executives.

BP also faced tough questions over a 2005 explosion at its refinery in Texas City, Texas, which killed 15 workers and injured 180 others.